A massive US surveillance blimp broke loose from its mooring Wednesday, sparking power outages as it drifted around Pennsylvania dragging a 6,600-foot cable before eventually easing down to Earth, officials said.

Two US F-16s fighter jets were scrambled to pursue the so-called JLENS blimp as it floated north of Washington at an altitude of about 15,000 feet (4,600 meters).

The North American Aerospace Defense Command (NORAD) said the huge balloon-like structure finally landed in Montour County in Pennsylvania, at around 4:00 pm (2000 GMT). A military recovery team was en route to collect the runaway aircraft.

NORAD spokesman Captain Scott Miller said a section of the aerostat's tail had broken off and plummeted to the ground. It wasn't immediately known if it caused any damage or injuries.

Authorities warned people to "remain clear" as power outages were reported in the town of Bloomsburg, Pennsylvania.

Local television said the cable attached to the helium-filled blimp had been "hitting power lines and causing blackouts" in Bloomsburg.

It came untethered from its mooring at Aberdeen Proving Grounds, an army installation in Maryland about 75 miles (120 kilometers) northeast of Washington, at around 12:20 pm (1620 GMT) while at an altitude of about 6,600 feet.

"People are warned to keep a safe distance from the airship and tether as contact with them may present significant danger," a statement from the Aberdeen Proving Ground said.

Weather conditions were within normal parameters for the craft to be in the skies.

The two F-16s that monitored the blimp were armed but "were never looking seriously at shooting (it) down," Miller said.

The aircraft was equipped with an auto-deflation system but it was not known if that had deployed.

JLENS blimps carry powerful radars that can monitor an area about the size of Texas for airborne threats including unmanned aircraft, cruise missiles and other objects.

The blimp normally flies at about 10,000 feet. When on the ground, it is tied down with a Kevlar-like cable a little more than an inch (2.5 centimeters) thick.

- $2.8-billion program -

Even before the current incident, the blimp's presence in the skies over the eastern United States had generated controversy.

Civil liberties activists worried the aircraft could be used for domestic surveillance, something the Pentagon strongly denies, saying the blimp cannot see people and has no cameras aboard.

Last year, the Government Accountability Office estimated the cost of the JLENS program at a whopping $2.8 billion so far. Congress, meanwhile, nearly halved JLENS' $54 million budget for fiscal 2015.

Nearly a decade in development, only two JLENS blimps are operational.

Together the pair make up an "orbit," with the ground crew of one aerostat assigned to 24/7 surveillance and the other tasked with directing air defense missiles to intercept a cruise missile in mid-flight.

Each blimp can stay aloft up to 30 days at a time, tethered to a dark green mobile mooring station, coming down to Earth only for maintenance -- like a fresh shot of compressed helium -- or extreme weather.

JLENS is a military acronym for "Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System."

The main JLENS contractor is Raytheon, which also makes the US military's sea-launched Tomahawk guided cruise missile.